Re: [PATCH 1/1] mm/pgtable/debug: Add test validating architecture page table helpers

[Anshuman Khandual]

On 09/04/2019 07:49 PM, Kirill A. Shutemov wrote:
> On Tue, Sep 03, 2019 at 01:31:46PM +0530, Anshuman Khandual wrote:
>> This adds a test module which will validate architecture page table helpers
>> and accessors regarding compliance with generic MM semantics expectations.
>> This will help various architectures in validating changes to the existing
>> page table helpers or addition of new ones.
>>
>> Test page table and memory pages creating it's entries at various level are
>> all allocated from system memory with required alignments. If memory pages
>> with required size and alignment could not be allocated, then all depending
>> individual tests are skipped.
> 
> See my comments below.
> 
>>
>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> Cc: Vlastimil Babka <vbabka@xxxxxxx>
>> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
>> Cc: Jason Gunthorpe <jgg@xxxxxxxx>
>> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
>> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
>> Cc: Mark Rutland <mark.rutland@xxxxxxx>
>> Cc: Mark Brown <broonie@xxxxxxxxxx>
>> Cc: Steven Price <Steven.Price@xxxxxxx>
>> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
>> Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
>> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
>> Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
>> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
>> Cc: Sri Krishna chowdary <schowdary@xxxxxxxxxx>
>> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
>> Cc: Russell King - ARM Linux <linux@xxxxxxxxxxxxxxx>
>> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
>> Cc: Paul Mackerras <paulus@xxxxxxxxx>
>> Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
>> Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
>> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
>> Cc: Vineet Gupta <vgupta@xxxxxxxxxxxx>
>> Cc: James Hogan <jhogan@xxxxxxxxxx>
>> Cc: Paul Burton <paul.burton@xxxxxxxx>
>> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
>> Cc: linux-snps-arc@xxxxxxxxxxxxxxxxxxx
>> Cc: linux-mips@xxxxxxxxxxxxxxx
>> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
>> Cc: linux-ia64@xxxxxxxxxxxxxxx
>> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
>> Cc: linux-s390@xxxxxxxxxxxxxxx
>> Cc: linux-sh@xxxxxxxxxxxxxxx
>> Cc: sparclinux@xxxxxxxxxxxxxxx
>> Cc: x86@xxxxxxxxxx
>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>>
>> Suggested-by: Catalin Marinas <catalin.marinas@xxxxxxx>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
>> ---
>>  mm/Kconfig.debug       |  14 ++
>>  mm/Makefile            |   1 +
>>  mm/arch_pgtable_test.c | 425 +++++++++++++++++++++++++++++++++++++++++
>>  3 files changed, 440 insertions(+)
>>  create mode 100644 mm/arch_pgtable_test.c
>>
>> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
>> index 327b3ebf23bf..ce9c397f7b07 100644
>> --- a/mm/Kconfig.debug
>> +++ b/mm/Kconfig.debug
>> @@ -117,3 +117,17 @@ config DEBUG_RODATA_TEST
>>      depends on STRICT_KERNEL_RWX
>>      ---help---
>>        This option enables a testcase for the setting rodata read-only.
>> +
>> +config DEBUG_ARCH_PGTABLE_TEST
>> +	bool "Test arch page table helpers for semantics compliance"
>> +	depends on MMU
>> +	depends on DEBUG_KERNEL
>> +	help
>> +	  This options provides a kernel module which can be used to test
>> +	  architecture page table helper functions on various platform in
>> +	  verifying if they comply with expected generic MM semantics. This
>> +	  will help architectures code in making sure that any changes or
>> +	  new additions of these helpers will still conform to generic MM
>> +	  expected semantics.
>> +
>> +	  If unsure, say N.
>> diff --git a/mm/Makefile b/mm/Makefile
>> index d996846697ef..bb572c5aa8c5 100644
>> --- a/mm/Makefile
>> +++ b/mm/Makefile
>> @@ -86,6 +86,7 @@ obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
>>  obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
>>  obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
>>  obj-$(CONFIG_DEBUG_RODATA_TEST) += rodata_test.o
>> +obj-$(CONFIG_DEBUG_ARCH_PGTABLE_TEST) += arch_pgtable_test.o
>>  obj-$(CONFIG_PAGE_OWNER) += page_owner.o
>>  obj-$(CONFIG_CLEANCACHE) += cleancache.o
>>  obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
>> diff --git a/mm/arch_pgtable_test.c b/mm/arch_pgtable_test.c
>> new file mode 100644
>> index 000000000000..f15be8a73723
>> --- /dev/null
>> +++ b/mm/arch_pgtable_test.c
>> @@ -0,0 +1,425 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * This kernel module validates architecture page table helpers &
>> + * accessors and helps in verifying their continued compliance with
>> + * generic MM semantics.
>> + *
>> + * Copyright (C) 2019 ARM Ltd.
>> + *
>> + * Author: Anshuman Khandual <anshuman.khandual@xxxxxxx>
>> + */
>> +#define pr_fmt(fmt) "arch_pgtable_test: %s " fmt, __func__
>> +
>> +#include <linux/kernel.h>
>> +#include <linux/hugetlb.h>
>> +#include <linux/mm.h>
>> +#include <linux/mman.h>
>> +#include <linux/mm_types.h>
>> +#include <linux/module.h>
>> +#include <linux/printk.h>
>> +#include <linux/swap.h>
>> +#include <linux/swapops.h>
>> +#include <linux/pfn_t.h>
>> +#include <linux/gfp.h>
>> +#include <linux/spinlock.h>
>> +#include <linux/sched/mm.h>
>> +#include <asm/pgalloc.h>
>> +#include <asm/pgtable.h>
>> +
>> +/*
>> + * Basic operations
>> + *
>> + * mkold(entry)			= An old and not a young entry
>> + * mkyoung(entry)		= A young and not an old entry
>> + * mkdirty(entry)		= A dirty and not a clean entry
>> + * mkclean(entry)		= A clean and not a dirty entry
>> + * mkwrite(entry)		= A write and not a write protected entry
>> + * wrprotect(entry)		= A write protected and not a write entry
>> + * pxx_bad(entry)		= A mapped and non-table entry
>> + * pxx_same(entry1, entry2)	= Both entries hold the exact same value
>> + */
>> +#define VADDR_TEST	(PGDIR_SIZE + PUD_SIZE + PMD_SIZE + PAGE_SIZE)
> 
> What is special about this address? How do you know if it is not occupied
> yet?

We are creating the page table from scratch after allocating an mm_struct
for a given random virtual address 'VADDR_TEST'. Hence nothing is occupied
just yet. There is nothing special about this address, just that it tries
to ensure the page table entries are being created with some offset from
beginning of respective page table page at all levels ? The idea is to
have a more representative form of page table structure for test.

> 
>> +#define VMA_TEST_FLAGS	(VM_READ|VM_WRITE|VM_EXEC)
>> +#define RANDOM_NZVALUE	(0xbe)
>> +
>> +static bool pud_aligned;
>> +static bool pmd_aligned;
>> +
>> +extern struct mm_struct *mm_alloc(void);
>> +
>> +static void pte_basic_tests(struct page *page, pgprot_t prot)
>> +{
>> +	pte_t pte = mk_pte(page, prot);
>> +
>> +	WARN_ON(!pte_same(pte, pte));
>> +	WARN_ON(!pte_young(pte_mkyoung(pte)));
>> +	WARN_ON(!pte_dirty(pte_mkdirty(pte)));
>> +	WARN_ON(!pte_write(pte_mkwrite(pte)));
>> +	WARN_ON(pte_young(pte_mkold(pte)));
>> +	WARN_ON(pte_dirty(pte_mkclean(pte)));
>> +	WARN_ON(pte_write(pte_wrprotect(pte)));
>> +}
>> +
>> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE
>> +static void pmd_basic_tests(struct page *page, pgprot_t prot)
>> +{
>> +	pmd_t pmd;
>> +
>> +	/*
>> +	 * Memory block here must be PMD_SIZE aligned. Abort this
>> +	 * test in case we could not allocate such a memory block.
>> +	 */
>> +	if (!pmd_aligned) {
>> +		pr_warn("Could not proceed with PMD tests\n");
>> +		return;
>> +	}
>> +
>> +	pmd = mk_pmd(page, prot);
>> +	WARN_ON(!pmd_same(pmd, pmd));
>> +	WARN_ON(!pmd_young(pmd_mkyoung(pmd)));
>> +	WARN_ON(!pmd_dirty(pmd_mkdirty(pmd)));
>> +	WARN_ON(!pmd_write(pmd_mkwrite(pmd)));
>> +	WARN_ON(pmd_young(pmd_mkold(pmd)));
>> +	WARN_ON(pmd_dirty(pmd_mkclean(pmd)));
>> +	WARN_ON(pmd_write(pmd_wrprotect(pmd)));
>> +	/*
>> +	 * A huge page does not point to next level page table
>> +	 * entry. Hence this must qualify as pmd_bad().
>> +	 */
>> +	WARN_ON(!pmd_bad(pmd_mkhuge(pmd)));
>> +}
>> +#else
>> +static void pmd_basic_tests(struct page *page, pgprot_t prot) { }
>> +#endif
>> +
>> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
>> +static void pud_basic_tests(struct page *page, pgprot_t prot)
>> +{
>> +	pud_t pud;
>> +
>> +	/*
>> +	 * Memory block here must be PUD_SIZE aligned. Abort this
>> +	 * test in case we could not allocate such a memory block.
>> +	 */
>> +	if (!pud_aligned) {
>> +		pr_warn("Could not proceed with PUD tests\n");
>> +		return;
>> +	}
>> +
>> +	pud = pfn_pud(page_to_pfn(page), prot);
>> +	WARN_ON(!pud_same(pud, pud));
>> +	WARN_ON(!pud_young(pud_mkyoung(pud)));
>> +	WARN_ON(!pud_write(pud_mkwrite(pud)));
>> +	WARN_ON(pud_write(pud_wrprotect(pud)));
>> +	WARN_ON(pud_young(pud_mkold(pud)));
>> +
>> +#if !defined(__PAGETABLE_PMD_FOLDED) && !defined(__ARCH_HAS_4LEVEL_HACK)
>> +	/*
>> +	 * A huge page does not point to next level page table
>> +	 * entry. Hence this must qualify as pud_bad().
>> +	 */
>> +	WARN_ON(!pud_bad(pud_mkhuge(pud)));
>> +#endif
>> +}
>> +#else
>> +static void pud_basic_tests(struct page *page, pgprot_t prot) { }
>> +#endif
>> +
>> +static void p4d_basic_tests(struct page *page, pgprot_t prot)
>> +{
>> +	p4d_t p4d;
>> +
>> +	memset(&p4d, RANDOM_NZVALUE, sizeof(p4d_t));
>> +	WARN_ON(!p4d_same(p4d, p4d));
>> +}
>> +
>> +static void pgd_basic_tests(struct page *page, pgprot_t prot)
>> +{
>> +	pgd_t pgd;
>> +
>> +	memset(&pgd, RANDOM_NZVALUE, sizeof(pgd_t));
>> +	WARN_ON(!pgd_same(pgd, pgd));
>> +}
>> +
>> +#if !defined(__PAGETABLE_PMD_FOLDED) && !defined(__ARCH_HAS_4LEVEL_HACK)
>> +static void pud_clear_tests(pud_t *pudp)
>> +{
>> +	memset(pudp, RANDOM_NZVALUE, sizeof(pud_t));
>> +	pud_clear(pudp);
>> +	WARN_ON(!pud_none(READ_ONCE(*pudp)));
>> +}
>> +
>> +static void pud_populate_tests(struct mm_struct *mm, pud_t *pudp, pmd_t *pmdp)
>> +{
>> +	/*
>> +	 * This entry points to next level page table page.
>> +	 * Hence this must not qualify as pud_bad().
>> +	 */
>> +	pmd_clear(pmdp);
>> +	pud_clear(pudp);
>> +	pud_populate(mm, pudp, pmdp);
>> +	WARN_ON(pud_bad(READ_ONCE(*pudp)));
>> +}
>> +#else
>> +static void pud_clear_tests(pud_t *pudp) { }
>> +static void pud_populate_tests(struct mm_struct *mm, pud_t *pudp, pmd_t *pmdp)
>> +{
>> +}
>> +#endif
>> +
>> +#if !defined(__PAGETABLE_PUD_FOLDED) && !defined(__ARCH_HAS_5LEVEL_HACK)
>> +static void p4d_clear_tests(p4d_t *p4dp)
>> +{
>> +	memset(p4dp, RANDOM_NZVALUE, sizeof(p4d_t));
>> +	p4d_clear(p4dp);
>> +	WARN_ON(!p4d_none(READ_ONCE(*p4dp)));
>> +}
>> +
>> +static void p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp, pud_t *pudp)
>> +{
>> +	/*
>> +	 * This entry points to next level page table page.
>> +	 * Hence this must not qualify as p4d_bad().
>> +	 */
>> +	pud_clear(pudp);
>> +	p4d_clear(p4dp);
>> +	p4d_populate(mm, p4dp, pudp);
>> +	WARN_ON(p4d_bad(READ_ONCE(*p4dp)));
>> +}
>> +#else
>> +static void p4d_clear_tests(p4d_t *p4dp) { }
>> +static void p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp, pud_t *pudp)
>> +{
>> +}
>> +#endif
>> +
>> +#ifndef __PAGETABLE_P4D_FOLDED
>> +static void pgd_clear_tests(pgd_t *pgdp)
>> +{
>> +	memset(pgdp, RANDOM_NZVALUE, sizeof(pgd_t));
>> +	pgd_clear(pgdp);
>> +	WARN_ON(!pgd_none(READ_ONCE(*pgdp)));
>> +}
>> +
>> +static void pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp, p4d_t *p4dp)
>> +{
>> +	/*
>> +	 * This entry points to next level page table page.
>> +	 * Hence this must not qualify as pgd_bad().
>> +	 */
>> +	p4d_clear(p4dp);
>> +	pgd_clear(pgdp);
>> +	pgd_populate(mm, pgdp, p4dp);
>> +	WARN_ON(pgd_bad(READ_ONCE(*pgdp)));
>> +}
>> +#else
>> +static void pgd_clear_tests(pgd_t *pgdp) { }
>> +static void pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp, p4d_t *p4dp)
>> +{
>> +}
>> +#endif
> 
> This will not work if p4d is folded at runtime. Like for x86-64 and s390.
> 
> Here's the fixup. It should work for both x86-64 and s390, but I only
> tested on x86-64:
> 
> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
> index 52e5f5f2240d..b882792a3999 100644
> --- a/arch/x86/include/asm/pgtable_64_types.h
> +++ b/arch/x86/include/asm/pgtable_64_types.h
> @@ -40,6 +40,8 @@ static inline bool pgtable_l5_enabled(void)
>  #define pgtable_l5_enabled() 0
>  #endif /* CONFIG_X86_5LEVEL */
>  
> +#define mm_p4d_folded(mm) (!pgtable_l5_enabled())
> +
>  extern unsigned int pgdir_shift;
>  extern unsigned int ptrs_per_p4d;
>  
> diff --git a/mm/arch_pgtable_test.c b/mm/arch_pgtable_test.c
> index f15be8a73723..206fe3334a28 100644
> --- a/mm/arch_pgtable_test.c
> +++ b/mm/arch_pgtable_test.c
> @@ -193,9 +193,11 @@ static void p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp, pud_t *pudp)
>  }
>  #endif
>  
> -#ifndef __PAGETABLE_P4D_FOLDED
>  static void pgd_clear_tests(pgd_t *pgdp)
>  {
> +	if (mm_p4d_folded(mm))
> +		return;
> +
>  	memset(pgdp, RANDOM_NZVALUE, sizeof(pgd_t));
>  	pgd_clear(pgdp);
>  	WARN_ON(!pgd_none(READ_ONCE(*pgdp)));
> @@ -203,6 +205,9 @@ static void pgd_clear_tests(pgd_t *pgdp)
>  
>  static void pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp, p4d_t *p4dp)
>  {
> +	if (mm_p4d_folded(mm))
> +		return;
> +
>  	/*
>  	 * This entry points to next level page table page.
>  	 * Hence this must not qualify as pgd_bad().
> @@ -212,12 +217,6 @@ static void pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp, p4d_t *p4dp)
>  	pgd_populate(mm, pgdp, p4dp);
>  	WARN_ON(pgd_bad(READ_ONCE(*pgdp)));
>  }
> -#else
> -static void pgd_clear_tests(pgd_t *pgdp) { }
> -static void pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp, p4d_t *p4dp)
> -{
> -}
> -#endif

This makes sense for runtime cases but there is a problem here.

On arm64, pgd_populate() which takes (pud_t *) as last argument instead of
(p4d_t *) will fail to build when not wrapped in !__PAGETABLE_P4D_FOLDED
on certain configurations.

./arch/arm64/include/asm/pgalloc.h:81:75: note:
expected âpud_t *â {aka âstruct <anonymous> *â}
but argument is of type âpgd_t *â {aka âstruct <anonymous> *â}
static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgdp, pud_t *pudp)
                                                                   ~~~~~~~^~~~
Wondering if this is something to be fixed on arm64 or its more general
problem. Will look into this further.

>  
>  static void pte_clear_tests(pte_t *ptep)
>  {
> 
>> +
>> +static void pte_clear_tests(pte_t *ptep)
>> +{
>> +	memset(ptep, RANDOM_NZVALUE, sizeof(pte_t));
>> +	pte_clear(NULL, 0, ptep);
>> +	WARN_ON(!pte_none(READ_ONCE(*ptep)));
>> +}
>> +
>> +static void pmd_clear_tests(pmd_t *pmdp)
>> +{
>> +	memset(pmdp, RANDOM_NZVALUE, sizeof(pmd_t));
>> +	pmd_clear(pmdp);
>> +	WARN_ON(!pmd_none(READ_ONCE(*pmdp)));
>> +}
>> +
>> +static void pmd_populate_tests(struct mm_struct *mm, pmd_t *pmdp,
>> +			       pgtable_t pgtable)
>> +{
>> +	/*
>> +	 * This entry points to next level page table page.
>> +	 * Hence this must not qualify as pmd_bad().
>> +	 */
>> +	pmd_clear(pmdp);
>> +	pmd_populate(mm, pmdp, pgtable);
>> +	WARN_ON(pmd_bad(READ_ONCE(*pmdp)));
>> +}
>> +
>> +static bool pfn_range_valid(struct zone *z, unsigned long start_pfn,
>> +			    unsigned long nr_pages)
>> +{
>> +	unsigned long i, end_pfn = start_pfn + nr_pages;
>> +	struct page *page;
>> +
>> +	for (i = start_pfn; i < end_pfn; i++) {
>> +		if (!pfn_valid(i))
>> +			return false;
>> +
>> +		page = pfn_to_page(i);
>> +
>> +		if (page_zone(page) != z)
>> +			return false;
>> +
>> +		if (PageReserved(page))
>> +			return false;
>> +
>> +		if (page_count(page) > 0)
>> +			return false;
>> +
>> +		if (PageHuge(page))
>> +			return false;
>> +	}
>> +	return true;
>> +}
>> +
>> +static struct page *alloc_gigantic_page(nodemask_t *nodemask,
>> +					int nid, gfp_t gfp_mask, int order)
>> +{
>> +	struct zonelist *zonelist;
>> +	struct zone *zone;
>> +	struct zoneref *z;
>> +	enum zone_type zonesel;
>> +	unsigned long ret, pfn, flags, nr_pages;
>> +
>> +	nr_pages = 1UL << order;
>> +	zonesel = gfp_zone(gfp_mask);
>> +	zonelist = node_zonelist(nid, gfp_mask);
>> +	for_each_zone_zonelist_nodemask(zone, z, zonelist, zonesel, nodemask) {
>> +		spin_lock_irqsave(&zone->lock, flags);
>> +		pfn = ALIGN(zone->zone_start_pfn, nr_pages);
>> +		while (zone_spans_pfn(zone, pfn + nr_pages - 1)) {
>> +			if (pfn_range_valid(zone, pfn, nr_pages)) {
>> +				spin_unlock_irqrestore(&zone->lock, flags);
>> +				ret = alloc_contig_range(pfn, pfn + nr_pages,
>> +							 MIGRATE_MOVABLE,
>> +							 gfp_mask);
>> +				if (!ret)
>> +					return pfn_to_page(pfn);
>> +				spin_lock_irqsave(&zone->lock, flags);
>> +			}
>> +			pfn += nr_pages;
>> +		}
>> +		spin_unlock_irqrestore(&zone->lock, flags);
>> +	}
>> +	return NULL;
>> +}
>> +
>> +static struct page *alloc_mapped_page(void)
>> +{
>> +	gfp_t gfp_mask = GFP_KERNEL | __GFP_ZERO;
>> +	struct page *page = NULL;
>> +
>> +	page = alloc_gigantic_page(&node_states[N_MEMORY], first_memory_node,
>> +				   gfp_mask, get_order(PUD_SIZE));
>> +	if (page) {
>> +		pud_aligned = true;
>> +		pmd_aligned = true;
>> +		return page;
>> +	}
>> +
>> +	page = alloc_pages(gfp_mask, get_order(PMD_SIZE));
>> +	if (page) {
>> +		pmd_aligned = true;
>> +		return page;
>> +	}
>> +	return alloc_page(gfp_mask);
>> +}
>> +
>> +static void free_mapped_page(struct page *page)
>> +{
>> +	if (pud_aligned) {
>> +		unsigned long pfn = page_to_pfn(page);
>> +
>> +		free_contig_range(pfn, 1ULL << get_order(PUD_SIZE));
>> +		return;
>> +	}
>> +
>> +	if (pmd_aligned) {
>> +		int order = get_order(PMD_SIZE);
>> +
>> +		free_pages((unsigned long)page_address(page), order);
>> +		return;
>> +	}
>> +	free_page((unsigned long)page_address(page));
>> +}
>> +
>> +static int __init arch_pgtable_tests_init(void)
>> +{
>> +	struct mm_struct *mm;
>> +	struct page *page;
>> +	pgd_t *pgdp;
>> +	p4d_t *p4dp, *saved_p4dp;
>> +	pud_t *pudp, *saved_pudp;
>> +	pmd_t *pmdp, *saved_pmdp;
>> +	pte_t *ptep, *saved_ptep;
>> +	pgprot_t prot = vm_get_page_prot(VMA_TEST_FLAGS);
>> +	unsigned long vaddr = VADDR_TEST;
>> +
>> +	mm = mm_alloc();
>> +	if (!mm) {
>> +		pr_err("mm_struct allocation failed\n");
>> +		return 1;
>> +	}
>> +
>> +	page = alloc_mapped_page();
>> +	if (!page) {
>> +		pr_err("memory allocation failed\n");
>> +		return 1;
>> +	}
>> +
>> +	pgdp = pgd_offset(mm, vaddr);
>> +	p4dp = p4d_alloc(mm, pgdp, vaddr);
>> +	pudp = pud_alloc(mm, p4dp, vaddr);
>> +	pmdp = pmd_alloc(mm, pudp, vaddr);
>> +	ptep = pte_alloc_map(mm, pmdp, vaddr);
>> +
>> +	/*
>> +	 * Save all the page table page addresses as the page table
>> +	 * entries will be used for testing with random or garbage
>> +	 * values. These saved addresses will be used for freeing
>> +	 * page table pages.
>> +	 */
>> +	saved_p4dp = p4d_offset(pgdp, 0UL);
>> +	saved_pudp = pud_offset(p4dp, 0UL);
>> +	saved_pmdp = pmd_offset(pudp, 0UL);
>> +	saved_ptep = pte_offset_map(pmdp, 0UL);
>> +
>> +	pte_basic_tests(page, prot);
>> +	pmd_basic_tests(page, prot);
>> +	pud_basic_tests(page, prot);
>> +	p4d_basic_tests(page, prot);
>> +	pgd_basic_tests(page, prot);
>> +
>> +	pte_clear_tests(ptep);
>> +	pmd_clear_tests(pmdp);
>> +	pud_clear_tests(pudp);
>> +	p4d_clear_tests(p4dp);
>> +	pgd_clear_tests(pgdp);
>> +
>> +	pmd_populate_tests(mm, pmdp, (pgtable_t) page);
> 
> This is not correct for architectures that defines pgtable_t as pte_t
> pointer, not struct page pointer.

Right, a grep on the source confirms that.

These platforms define pgtable_t as struct page *

arch/alpha/include/asm/page.h:typedef struct page *pgtable_t;
arch/arm/include/asm/page.h:typedef struct page *pgtable_t;
arch/arm64/include/asm/page.h:typedef struct page *pgtable_t;
arch/csky/include/asm/page.h:typedef struct page *pgtable_t;
arch/hexagon/include/asm/page.h:typedef struct page *pgtable_t;
arch/ia64/include/asm/page.h:  typedef struct page *pgtable_t;
arch/ia64/include/asm/page.h:    typedef struct page *pgtable_t;
arch/m68k/include/asm/page.h:typedef struct page *pgtable_t;
arch/microblaze/include/asm/page.h:typedef struct page *pgtable_t;
arch/mips/include/asm/page.h:typedef struct page *pgtable_t;
arch/nds32/include/asm/page.h:typedef struct page *pgtable_t;
arch/nios2/include/asm/page.h:typedef struct page *pgtable_t;
arch/openrisc/include/asm/page.h:typedef struct page *pgtable_t;
arch/parisc/include/asm/page.h:typedef struct page *pgtable_t;
arch/riscv/include/asm/page.h:typedef struct page *pgtable_t;
arch/sh/include/asm/page.h:typedef struct page *pgtable_t;
arch/sparc/include/asm/page_32.h:typedef struct page *pgtable_t;
arch/um/include/asm/page.h:typedef struct page *pgtable_t;
arch/unicore32/include/asm/page.h:typedef struct page *pgtable_t;
arch/x86/include/asm/pgtable_types.h:typedef struct page *pgtable_t;
arch/xtensa/include/asm/page.h:typedef struct page *pgtable_t;

These platforms define pgtable_t as pte_t *

arch/arc/include/asm/page.h:typedef pte_t * pgtable_t;
arch/powerpc/include/asm/mmu.h:typedef pte_t *pgtable_t;
arch/s390/include/asm/page.h:typedef pte_t *pgtable_t;
arch/sparc/include/asm/page_64.h:typedef pte_t *pgtable_t;

Should we need have two pmd_populate_tests() definitions with
different arguments (struct page pointer or pte_t pointer) and then
call either one after detecting the given platform ?

> 
>> +	pud_populate_tests(mm, pudp, pmdp);
>> +	p4d_populate_tests(mm, p4dp, pudp);
>> +	pgd_populate_tests(mm, pgdp, p4dp);
> 
> This is wrong. All p?dp points to the second entry in page table entry.
> This is not valid pointer for page table and triggers p?d_bad() on x86.

Yeah these are second entries because of the way we create the page table.
But I guess its applicable only to the second argument in all these above
cases because the first argument can be any valid entry on previous page
table level.

> 
> Use saved_p?dp instead.

It works on x86. Will test on arm64 and update.